To improve penetration, which choice would you make regarding transmitted frequency?

• A. Use a lower transmitted frequency to improve penetration (and accept reduced Doppler sensitivity)
• B. Use a higher transmitted frequency to improve penetration
• C. Frequency has no effect on penetration
• D. Penetration depends only on tissue type

Answer: (A)

Penetration is mainly limited by attenuation, which grows with frequency. By using a lower transmitted frequency, the ultrasound wave experiences less attenuation as it travels through tissue, so deeper structures can be reached and their echoes can return to the transducer. The trade-off is worth noting: lower frequencies reduce axial and lateral resolution and also weaken Doppler sensitivity, since the Doppler shift decreases with frequency. So choosing a lower frequency improves depth at the cost of finer detail and velocity measurement precision.